Rotary out-trunk switching arrangement



5 Sheets-Shea?. 1

O. C. HALL ROTARY OUT-TRUNK SWITCHING ARRANGEMENT L SMQ SSE Sept. 2, 1952 Filed Aug. 9, 195o M11/wmp 0. C. HALL BV ATTORNEY Sept. 2, 1952 o. c. HALL ROTARY OUT-TRUNK SWITCHING ARRANGEMENT 3 SheetAs-Shee. 2

Filed Aug. 9, 195o Sept. 2, 1952 o c. HALL 2,609,455

ROTARY OUT-TRUNK SWITCHING ARRANGEMENT Filed Aug. 9, 1950 3 SheetsSheet 3 Y /A/l/EN'OR 0. C. HALL BV WQCM@ ATTORNEY Patented Sept. 2, 1952 Oliver C.

, ARRANGEMENT n Hall, Fair Lawn, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. .-a corporation of New York `Applicationaugust 9, 195o, serial No. 178,518

This invention relates to communica ion systems "and particularly to switchingsysteins employingnon-numerical trunking switches.

Objects of the invention are the distribution 'of traic from a number ofvsmall trunk groups overa single large group of trunks, ther-.oneentration of traic from a large number of trunks to a1 lsmaller number of trunks and a more eiiicientk and otherwise improved operation of non-numerical trunking switches.

This invention is anon-numerical trunking switch arranged to preselect an idle outgoing trunk, `to make a selected outgoing'ftrunk test busy to other trunking switches or other selectors having access thereto as soon as the trunking switch is seized by a preceding switch'andto stop the trunk hunting-"operation when all Voutgoing trunks `to which the switch has accessbecome busy. A feature of the invention is the provision of a, separate set of terminals in a preselecting outgoing trunking switch on which the'brushes of the switch come to rest so as to bring in an alarm in case the switch trunk hunts continuouslygfor a predetermined interval of-itime or in case the switch is seized while its brushes .are in engagement with said set of terminalsfAnother feature is a preselecting outgoing trunking switch arranged to mark the trunk incoming? to the switchso that this incoming trunk tests:busy to all preceding switches having access thereto.

v#'Ih'e' invention and its features, including those mentioned, are embodied in the systemshown schematically inthe drawings. The invention is not'yLhowevei, limited in its applicationyto the particular system disclosed but is generally, applicableto any system employing outgoing-trunking switches. i: f

Referring to the drawing, Figfal shows in an automatic telepho ve office 20, line finder, selector and connector switches for establishing connections between calling vand called subscriber lines, and a rotary out trunk switch OTS-I; Y l

Fig. V2 shows in theautomatic oilce 20, another rotary out trunk switchOTS-Z and an auxiliary trunk circuitV lill;V and shows in another automatic oiice l0, line nder and selector switches and automatic ticketingV trunk and sender circuits;

Fig. 3 shows inthe automatic o'ice 2|) an out-4 going trunk4 circuit 80 associated with an outgoing trunk O'AI| leading to a step-by-step office 90; and shows in the step-by-step oice 90 an incoming selector 9|, a connector 95 4and a subscribers line Lillo; and

Fig. 4 shows lthe relative Aposition in which rclaims. (CL 179-18) Figs. 1, 2 and 3 are to be'placed to form an operative system. l

The switching equipment in offices Il) and 20 may be any known type but is shown as being of the step-by-step type. The subscriber stations 2|, 21 and |00 are of known type including a dial for useA in controlling selector and connector switches. Reference may be had to Automatic Telephony by Smith and Campbell, 2nd edition, published in1921, pages'53 to 69 for a description of the structure o1' step-by-step switches and their operation when used as selectors and connectors. Reference may be had to Patent 1,799,654, granted April 7, 1931, to R. L. Stokely, for a description of the operation of such switches when used as line nders. The line nder switches |2 and 23, selector switches I3, 24, 25 and 9| and connector switch 26 are each represented by a set of brushes and one or two sets of terminals, all other associated equipment being omitted. The connector switch. 95 is represented by a set of brushes and a single set of terminals; and the associated connector circuit apparatus is represented by line relay 96, release relay 91, condensers 98, and supervisory relay 99,

sender circuit I5 is similar to the sender circuit shown in Figs. 6 to 10 of the Retallack patent and in Figs. 30 to 43, inclusive, of said Gooderham application. The automatic ticketing trunk circuit |4 is represented by the repeating coil B04' and supervisory relay 8|3, and the sender circuit l5 is represented by relay 32| and 3900, each of these elements having the same reference characters as the corresponding elements in the Gooderham specication. The rotary out-trunk switch .circuits OTS-l and vOTS-2, the auxiliary trunk circuit 50 and the outgoing trunk circuit are shownfin detail and the operation of each is fully set forth herein.

The rotary out-trunk switch circuitJ OTS-I comprises a 22-point rotary switch having a stepping magnet 40, brushes and terminal banks 4|, 42, 43 and 44, a stepping relay 3| and a sleeve relay 32. The rotary outa-trunk circuit OTS-2 comprises a 22-point rotary switch having a stepping magnet 70, brushes and termina1 banks 7|, 12, 13 and 74, a stepping relay 6| and a sleeve relay| 2. rReference may be had to Patent 1,472',- :465vgranted October 30, 1923, to O.y F. Forsberg,

terminates in an incoming selector circuii-SI inV In the oce 2U, each trunk of theoice gil. group leading to oice 90 is connected to an cutgoing trunk circuit similar tothe trunk circuit I 8B to which trunk OTI is individually connected, this trunk circuit being arranged to repeat selective impulses over the trunk to control the operation of the switches in oce 90. As illustrated, the trunk circuit A8l) is connected by conductors 45, 46 and lll tothe first set of terminals in the bank of a group of out-trunk switches including the switch OTS-l, each of which is directly connected toa set of'terminals inthe bank .of a selector switch in oilice 42l); and the trunk circuit 88 is also connected by `conductors 15, 'I6 and 1'.' to the rlrst set of. terminals in the banks of another group of switches including the switch OTS-2, each of which is connected to anauxiliai-y.- trunk circuit such as Scand which is,V in turn, connected by a trunk i6 to an automatic ticketing trunk circuit I4 in office i6." This arrangement makes thesingle group of trunks from office 2i) to oiiice S0 available for use in completing calls originating in lboth oices i8 and 28. The system may require other groups of out-v trunk switches and the trunking arrangement may be one in which all of the out-trunk switches in a group are connected directly to outgoing trunks; ,and may beone4 in which all ofthe out, trunk switches in a group are directly connected to terminals in the banks of Selectors, orare drectly connected to automatic ticketing Atrunk circuits, or are directly connected to auxiliary trunks which, in turn, are connected by ,intercnice trunks to automatic ticketing trunk circuits in another oce.

Each rotary out-trunk switch is preselecting andstays in the position last used untilthe trunk connected to the terminals engaged by the brushes is seized by some other switch, whereupon any such switchis advanced, in the manner hereinafter described, Vuntil the brushes engage terminals connected to an idle trunk; or, incase all trunks are then busy, any such switch is advanced to position 2v2, in which position the' brushes remain until a trunk becomes idle.

Each group of rotary out-trunk switches has associated therewith alarm relays, such as relays relaysl 43 and 'I8 for each trunk which is multipled to the banks of the group of out-trunk switches;

trunk group relays, suchas relays 38 and 68;V

and one or more all-trunks-busy relays, suchv as relay 69. The function andA voperation of the alarm, trunk and trunk group relays are hereinafter described.

Assume rst that each of switches OTS-l and:v

OTS-2 are idle, that the brushes of switchOTS-I are in position I and that the brushes of switchY OTS-2 are in any position other than position22.

Assume further that a call is originated atstation 2 I, that the line L2l is thereupon connected by a line `finder switch -2-3 to a rst selector switch 24 and thatA the selector 24 is operated underthe A control of dial impulses from the calling station to make a group selection and then automatically to select the set of terminals to which conductors 28, 29 and 30 are connected. Upon selection of this set of terminals, ground potential is connectedY through the testbrush of selector 24 to conductortcausing the energization of the right winding of sleeve relay 32 and the energization of the winding of the trunk relay 48 associated 1o' with the outgoing trunk circuit 8i). Relay 32 operates and locks through its left winding and left front contact to the grounded conductor 30 before relayfdll operates to open the shunt circuit through' resistor 49. The operation of relay 32 @opens the connection between the winding of stepping relay 3| and the test brush 44 to prevent stepping of the brushes. The operation of relay 4,8connects ground to terminal l of each switch in the group, thereby to effect the operation of the stepping relay of any other out-trunk switch in the same group which happens at that time to have its brushes in engagement Ywith terminals l, and to guard against seizure ofthe out-trunk circuit il'by any other of the switches which may trunk hunt while trunk circuit 8D is busy on the,l call incoming through switch OTS-I. .The connection from the calling line to conductors 28 and 29 is extended through brushes .4,2 and 43, conductors'cl and 46 and right back contacts ofl relay, 84 .of outgoing trunk circuit 88 to-the windings of relay 8l, thereby operating relay 8|. The operation of relay 8l closes a circuit foroperating the slow-to-release relay 82; and relay 82 connectsI groundto sleeve conductor 4l to maintain the energization of relay 48. The ground thus, connected to conductor4l is further connected,throughbrushfll andthe right front Contact of relay 32 tothe left winding of relay 372 to hold relayV 32;.operated after themomentary ground in the selector circuit 24 'is disconnected from sleeve conductor 3 8; and this ground is further connected through the left front contact of krelay 32 and .a normally closed contactof jack MBI to conductor 38 to hold the connection established through switches 23 and 24 between line L2I and switch OTS-l'.- The ground connected to sleeve conductor 4l is further conf nected through back contacts of relays 86 and`85 and sleeve conductor'l'l 'to terminal l of eachv of the out-trunk switches in the group including switch OTS-2, thereby operating trunk relay 18. The Aoperation of relay-`l8 connects ground Y tof terminal l of bank 14 of each switch in the group including switch OTS-2; so that the stepping relay and stepping magnet of any switch-standing in position l is operated to elect the advance of such a switch to hunt vfor anidle set of -terminals; and so that none of these switches will stopin position l' whiletrunk circuit 80 is busy The operation'of relay 82 closes a circuit for energizing the biasing winding of supervisory relay 84. -'The aforementioned operation of relay 8l closes a bridge across conductors 88-and 89 of trunk OT-l to operate the une relayk (not shown) of incoming.

selectorf l. Ilhis bridge is traced from conductor 88- through a normally closed contact of' relay 83, left winding of relay 84, another normally closed contact of relay 83 and inner right front contactof relay 8|, to conductor 88. The cur-- rent through the left winding of relay 84 isfat this time in the non-,operating direction s'othat relay 84 does not operate. vWhen the calling subscribers directory number, relay Bl is alternately released and reoperated responsive to each impulse in the train of pulses created by the pulsing contacts of the dial. The release of relay 8| at thev beginning of the iirst pulse closes a circuit foroperating relay 83. Being slow to release, relay 82 remains operated during the transmission of dial pulses; and since relay 83 is slow to release, it remains operated until all of the pulses in a Vdigit train have been transmitted.. Each time relay 8| releases, it cause the release of the line vrelay (not shown) of selector 9|; and each time relay 8 I ,reoperates, battery and ground are connected through front contacts of relay 83 and front contacts of relay 8| to conductors 88 and 89, respectively, to effect the reoperation of the line relay of selector 9|. At the end of the pulse trainrelay 8| remains operated long enough to cause the release of relay 83, whereby theleft winding of relay 84 is again bridged-across conductors 88 and 89. The selector 9| selects a trunk to an idle connector, whereby the line relay 9,6 is operated in series with the left winding of relay 84. The operation of relay 96 causes the operation-of slow-to-release relay 91; and relay 91 connects ground to conductor 94 to hold the connection established through selector 9|, in usual manner. The trainsof pulses created by the dialing of the remaining digits of the called subscribers directory number are transmitted by relay 8| over trunk OT-l to line relay 95, whereby the connector is operated to extend the connection to the called line LIDD. The called station is signaled by means not shown; and, when the call is answered, relay 99 operates, thereby effecting a reversal of current over the conductors of trunk OT-l and operation of relay 84. Relay 84 in turn interchanges the connection between conductors 45 and 46 and the windings of relay 8| to reverse the current in conductors 23 and 29. When the called subscriber replaces the telephone set at station |00, relay 99 releases; and when the calling subscriber replaces the telephone set at station 2 I, rel-ay 8| releases. The release of relay 8| opens the bridge across conductors 88 and 89, to effect the release of relay 96. Relay 91 is thereby released to disconnect ground from conductor 94;" and the selector 9| and connector 95 are thereupon restored to normal in usual manner. Relay 82 releases, following the release of relay 8|, thereby disconnecting ground from conductors 41, 11'and 38, eiecting the release of trunk relay 48, the release of sleeve relay 32, and the return of the selector 24 and line finder 23 to normal in usual manner. The release, of relays 48 and 18 disconnects ground from terminal of bank 44 of each of the switches in the groups including switches OTS-I and OTS-2, thereby makingthe terminals to which trunk circuit 80 is connected selectable by any out-trunk switch of eithergroup.

Incase the brushes of switch OTS-I are in position at the time that trunk circuit 8|! is seized on a call through some other switch in the group, the connection of ground to conductor 41 in the manner above described causes the operation .of trunk relay 48'. The operation of relay 48 closes a circuit from ground through the front contact of relay 48, terminal and brush 44, left back contact of relay 32, back contact of stepping magnet 40, resistor 33 and winding of stepping relay 3|. Relay 3| operates, closing a circuit for operating stepping magnet 40. The operation of stepping magnet 48 causes the release of relay 3|, and the release of relay 3| causes the releasev of stepping magnet 40 thereby advancing the brushes to the next set of terminals. If the trunk to which this next set of terminals connects is also busy, the trunk relay similar toirelay 48 is operated and stepping relay 3| is reoperated to effect the reoperation of stepping magnet 40 and advance of the brushes another step. This action, is repeated until the brushes engage a set of terminals connected to an idle one of the trunks, to which switch OTS-I has access. The switch does not stop in position 22 if any of these trunks is idle because terminal 22 of bank 44 is connected to ground at a front contact of normally operated group relay 38. In case all trunks to which switch OTS-I has access are busy, allof the trunk relays such as relay 48 are operated, causing the release of group relay 38; and in this case, ground is disconnected from terminal 22 of bank 44 and the brushes are advanced toand remain in position 22. When a trunk becomes idle, the associated trunk relayreleases, thereby causing the reoperation of, group relay 38, the operation of stepping relay 3| and stepping magnet 40 and the advance of the brushes to the idle set of terminals.

Assume next that a call is initiated ata station in oice |0, that the line L|| is extended by a line finder |2 to a rst selector I3 and, .under the control of the dial at station to an automatic ticketing trunk I4 and sender |5. Reference may be had to the aforementioned patent to J. B. Retallack and application of J. W. Gooderham for a detailed description of .the operation of the automatic ticketing trunk and sender circuits. When the sender |5 is connectedy to the automatic ticketing trunk I4, the sender connects the middle winding of relay 32| across the conductors of trunk I6; and, assuming that f the brushes of out-trunk switch OTS-2 are in position I, relay 5| of auxiliary trunk circuit AT and relay 8| of outgoing trunk circuit 8|)` are operated in the pulsing circuit which is further traced from the conductors of trunk IB, windings of relay 5|, back contacts of relay 55, conductors 58 and 59, brushes 12 and 13, conductors 16 and 15, winding of relay 86 of outgoing trunk circuit 88. back contacts of relay 85, back contacts of relay 84 and the windings of relay 8|. The current in this circuit causes the operation of relay 32| in sender circuit |5 and also relays 5|, 86 and 8|. The operation of relay` 5| closes a circuit for operating slow-to-release relay 52; and the operation of relay 52 closesa circuit from ground at the back contact of relay 53, through the right front contact of relay 52, sleeve conductor 60, back contact of jack MB2, right winding and back contact of relay 62, brush 1|, conductor 11, back contact and winding of relay 18, to battery. Relay 62 operates and closes a holding circuit through its left winding before relay 18 operates and opens the shunt circuit through resistor 19. The operation of relay 62 opens the connection between the winding of stepping relay 6| and brush 14 to prevent stepping of the brushes. The operation of relay 18 connects ground to terminal of .bank 14 of each switch in the same group, thereby to eiect the operation of the stepping relay of any other outtrunk switch in the group which happens at that time to have its brushes in position and also to guard against seizure of the outgoing trunk circuit by any other of the out-trunk switchesv which may trunk hunt while trunk circuit 80,

is busy on the call incoming through switch OTS-2. The aforementioned operation of relay 8| closes a circuit for operating relay 82; and

relay 82 connects ground to conductor 41 to operate trunk relay 48 to cause trunk hunting by each switch in the group including switch OTS-I having its brushes in position I at the time relay 82 of trunk circuit 8D is operated. With relay 86 operated, the operation of relay B2 does not connect ground to conductor 11; but relay 18 is held operated in series with the right winding ofi-relay 62, through conductor and a front contact of relay 52 to ground at the back contact of relay 53 of the auxiliary trunk circuit 5D. The ground connected to conductor 41 is further connected to terminal I of bank 4I of each of the other out-trunk switches in the same group lbut without effect since none of these other switches will stop in position I while relay 48 is operated. The operation of relay 82 closes a circuit for energizing the biasing winding of supervisory relay 84, and closes a circuit including vthe front contact of relay 86 for operating relay 85. Relay 85 locks under the direct control` of relay 82, opens the circuit through the winding of relay 85 and interchanges the connections between conductors 16 and 15 and the windings of relay 8l to reverse the .current in the pulsing circuit and thereby cause the release of relay 32H in sender circuit l5. Relay 85 releases but, with relay 85 operated, the ground connected by relay 82 to conductor 41 .is not connected to conductor 11. The release of relay 32II of sender circuit I5 causes the sender to transmit trains of pulsesto relay 8|` and vthese pulses are repeated by relay 3l over trunk OT-I to effect the completion of the desired .connection in office 9U.

vWhen the telephone is restored to normal at station II, the automatic ticketing trunk circuit I4 opens the repeating coil bridge across the conductors of trunk I6 and the trunk circuit hi, selector I3 and line nnder l2 are restored to normal. The opening of the bridge acrossthe conductors of trunk I8 causes the release ofrelays 5I and 8i. The release ofrelayEl causes the release of relay 52; and the release of relay 8| causes the release of relays 82 and 85 in succession and causes the release of `relays-S5 and 91 in succession. The release of relay 82 disconnects ground potential from conductorv 41-re leasing relay 48, and the release of relay 51 disconnects ground from conductor 94, the incoming selector 9i and connector B5 being'- restored to normal in usual manner. The aforementioned release of relay 52 transfers sleeve conductor 50 from-ground at the back contact of relay 53 to the winding of `relay 53, therebyl causing the release of relays62- and 18. The release of relays 48 and 18 disconnects ground potential from terminal l `of banks 4s and 'Myand the brushes of switches OTSAV and OTS-f2 remain-'in position-I until trunk circuit 8i) is'seized by some tion of ground "toconductor 11, causes theoperation of stepping lrelay ESI; and thebrushes Aof switch OTS-2 are thereby advancedlto hunt-for anidle trunk. In this case, the `connection of ground to conductor'l is also effective to cause the operation of relay 53 of auxiliary trunk circuit5Il; but relay S2 is not operated in series with relay 53 since its right winding is shunted by rectifier G4. The operation "of relay 53 closes a circuit for operating relay 55. The operation of relay 55 closes a locking circuit for relay 53 to sleeve conductor 60, independent of -relay 52 disconnects conductors 58 and 59 from the windings of relay 5I and connects battery and ground through the windings of retard coil 56 tothe windings of relay 5 i. Thus the automatic ticketing trunk circuit I4 may be seized while out-trunk switch OTS-2 is hunting for an idle trunk, but the connections between trunk I6 and brushes 12 and 13 of switch OTS-2 are open until 1an idle trunk is found. In case trunk circuit I4 is seized while switch OTS-2 is'trunk hunting and relays 53 and 55 are operated, relays 5I and 52 are operated in succession. If there is an idle trunk when relay 52 operates, relay 53 releases as soon as the brushes of switch OTS-*2 engage the idle set of terminals; whereupon the release of relay 53 causes the release of relay 55 thereby connecting trunk I6 through conductors 58-and 59 and brushes 12 and'13 to the idle trunk circuit. If all trunks to which switch OTS-2 has-access are busy, all trunk relays such as 18 are operated and relay 68 releases. The release of relay S8 closes a circuit for operating relay 59 and disconnects ground from terminal 22 of bank 14 of each switch in the group, so that all idle switches in the group are advanced to and stop in position r22. If relay 69 is operated while switch OTS-2 is hunting and relays 53 and 52 are operated as above described, a circuit is closed through conductor 51 for operatingrelay 54. Relay 54 locks under the sole control of relay 52, closes a connection for holding relay 55 operated independent of relay 53, and connects busy tone source BT to one winding of retard coil 56 thereby transmitting trunks-busy tone to vthe calling station.

If the trunk circuit 88 is seized by some other switch in the group including switch OTS-2 While the brushes of switch OTS-2 are standing in position I, relay 18 is operated (in the manner above described when switch OTS-2 is seized) and the operation of relay v'I8 connects ground to terminal I of bank 14 to operate stepping relay 6I and thereby ei'lect the advance of the brushes to the next set of terminals, the operation of` stepping relay '6I being repeated until an idle set of terminals is encountered.

. If the tip and ring conductors 28 and '29, leading to brushes 42 and'43 of switch OTS-I, should become short-circuited :or if ring conductor 28 should become grounded while the switch is engaging an idle set of terminals, the outgoing trunk circuit, for instance trunk circuit 80, connects ground to sleeve conductor 41 operating trunk relay 48; and the operation of relay 48 causes the operation of the stepping relay .3| and stepping magnet 48 to advance the brushes, these operations being repeated until the brushes I reach position 22. In this position, Ystepping relay 3l is held operated by the short-circuitl or ground so that stepping magnet 4e is held operated and-the brushes remain in position 22. When the trouble is clearedrelay 3| releases and-the stepping magnet 40 then releases, advancing the brushes to hunt for an idle set of terminals. AEach time the stepping relay 3|,.of anyswitch inthe group including switch OTS-I, is operated, a circuit is closed for operating the common alarm relay 36; and, if the stepping relay remains operated for a predetermined interval of time, due to a short-circuit on ground, asabove mentioned, or because the selector trunk hunts continuously, or because of .any other troublecondition, an alarm 311s operated. 1n

geballte ,9. l like` mannen'a short-circuit acrossv conductors 58 and 59 leading to theA brushes 12 and 13j of switch OTS-2 Vor a ground on conductor58j will cause operation ofthe trunk relay s'uchas relay l8 and advance of switch OTS-2v to position -22; and with stepping relay V6| held ,operated in position 22, an alarm relay 66 is operated and after a predetermined interval of time, an alarm 6l is operated. When the trouble is cleared, relay 6| releases and stepping magnet ,10V releases, advancing the brushes to rhunt for" an idle set of terminals. I?

In case the sleeve or the sleeve relay 62 of switch OTS-2 should become operated for any reason while the brushes are inposition 22, the release oflrelayjS or v6.8 when some trunk becomes idle could not cause the operation of stepping relay 3l or 6I; and the switch or switches in question could not advance out of position 22. However, in this case, alarm relay 35 or alarm relay 65 is operated in series with the left Winding of relay 32 or 62, thereby closing a circuit for operating alarm relay 36 or 66 to bring in an alarm after a predetermined interval. The sleeve relay 32 or 62 may then be released by manually opening the right front contacts of the relay so the stepping relay may operate when the trunk group relay releases.

What is claimed is:

1. In combination in a telephone system comprising a plurality of central oices each including switching means for completing conversational connections between calling and called subscriber stations, a plurality of rotary switches each comprising a plurality of wipers and sets of terminals and means for advancing the wipers from each set of terminals to the next, a group of outgoing trunks extending to one of said offices, each of said trunks connected to one of the sets of terminals in each of said rotary switches, auxiliary trunk circuits, one for each of said switches, incoming trunks, each of said incoming trunks connected to a different one of said auxiliary trunk circuits, relay means individual to each outgoing trunk operated when the trunk is busy, means individual to each of said switches for effecting the advance of the switch to the next set of terminals responsive to operation of said relay means associated with the trunk connected to the set of terminals engaged by the Wipers of the switch when this trunk is seized through another of said switches, means in each of said vtrunk circuits normally connecting the associated incoming trunk to the Wipers of the associated rotary switch and therethrough to onev of said outgoing trunks, means associated with each outgoing trunk eiective when an incoming trunk to which it is connected is seized for operating said relay means individual to said outgoing trunk, and means comprising relay means in the auxiliary trunk circuit associated with the seized incoming trunk rendered effective in case the rotary switch is being advanced at the time the incoming trunk is seized for opening the connection between sad incoming trunk and the wipers of the associated rotary switch.

2. In combination in a telephone system comprising a plurality of central oices each including switching means for completing conversational connections between calling and called subscriber stations, a plurality of rotary switches each comprising a plurality of wipers and sets of terminals and means for advancing the wipers from each set of terminals to the next, a group of outgoing trunks extending to one of said oices, each of said trunks connected to one of the sets of termirelay 32` of switch OTS-l nals in each .of said rotary switches, auxiliary trunk circuits,` one for each of said switches, incoming trunks, each ofl said. incoming trunks connectedl to a different one of Asaid auxiliary trunk `circuitsr elay means individual to4 each outgoing trunk operated when the trunk is busy, means individual to each'of said switches for effecting the advancelof the switch to the next set of. terminals responsive to operation of said relay .means associated with the trunk connected tothe set ofterminals engaged by the wipers of the switchy when this trunk is seized through-anotherfof said switches, means in each of said trunk circuits Anormally connecting the associ` ated incoming trunk to the Wipersof the associated rotary switch and therethrough to one of said outgoing trunks, means associated with each outgoing trunk effective when an incoming trunk to which it is connected is seized for operating said relay means individual to said outgoing trunk, and means comprising relay means in the auxiliary trunk circuit associated with the seized incoming trunk rendered effective in case the rotary switch is being advanced at the time the incoming trunk is seized for opening the connection between said incoming trunk and the wipers of the associated rotary switch, and means including relay means associated with said group of outgoing trunks and relay means in the auxiliary trunk circuit associated with the seized incoming trunk rendered eiective when all of the outgoing trunks are busy for holding open the connection between the incoming trunk and the wipers of the associated rotary switch until the incoming trunk is released.

3. In combination in a telephone system comprising a plurality of central oices each including switching means for completing conversational connections between calling and called subscriber stations, a plurality of rotary switches each comprising a plurality of wipers and sets of terminals and means for advancing the wipers from each set of terminals to the next, a group of outgoing trunks extending to one of said oflices, each of said trunks connected to one of the sets of terminals in each of said rotary switches, auxiliary trunk circuits, one for each of said switches, incoming trunks, each of said incoming trunks connected to a diierent one of said auxiliary trunk circuits, relay means individual to each outgoing trunk operated when the trunk is busy, means individual to each of said switches for effecting the advance of the switch to the next set of terminals responsive to operation of said relay means associated with the trunk connected to the set of terminals engaged by the wipers of the switch when this trunk is seized through another of said switches, means in each of said trunk circuits normally connecting the associated incoming trunk to the wipers of the associated rotary switch and therethrough to one of said outgoing trunks, means associated with each outgoing trunk eiective when an incoming trunk to which it is connected is seized for operating said relay means individual to said outgoing trunk, means comprising relay means in the auxiliary trunk circuit associated with the seized incoming trunk rendered effective in case the rotary switch is being advanced at the time the incoming trunk is seized for opening the connection between said incoming trunk and the wipers of the associated rotary switch, each of said rotary switches having one set of terminals to which no outgoing trunk is connected, and relay means effective to normally mark said one set of terminals as busy and 11 eiective Whenall of said outgoing trunksare busy to remove said busy markingvthereby to prevent the further advance ofthe Wipers as long, as the al1-busy. condition continues to exist.

4. In a muitioiee telephone system, subscriber lines, outgoing trunks, outgoing from one oiiice, incoming trunksincomingto said one office, rotary'switches, one for each incoming trunk,.each of said outgoing trunks connectedt'o a different set of terminals in the bank of each of said switchesmeans.for connecting a calling one of said subscriber lines to an idle one of said incoming trunks, means associated with each incoming trunk eiective when a calling subscribers line is connected thereto and the Wipers of the associated rotary. switch are connected to an idle' one of said outgoing trunks for'marking saidlincoming, trunk as. busymeans in each.. switch eilr festive whenY tiie-4 wipers are engaging a, busy outgoing. trunk for. causingA theyadvance of; the wipersl to. the nextl set of. terminals; another. set o'f terminals in. the bankfofeach switchnormally markedbusy.. and,- means for removing -saidl busy marking fromfsaid othersetcof terminals when all of said outgoing-trunks are busy..

n OLIVER @HALL REFERENCES CITEDu The following references are of recordiinthe Number Date,

Gardner ....-.Q Aug,: 14, 1928 

